The patch below does not apply to the 3.16-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From abe5f972912d086c080be4bde67750630b6fb38b Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@xxxxxxxxxxx>
Date: Thu, 2 Oct 2014 16:21:10 -0700
Subject: [PATCH] mm: page_alloc: fix zone allocation fairness on UP
The zone allocation batches can easily underflow due to higher-order
allocations or spills to remote nodes. On SMP that's fine, because
underflows are expected from concurrency and dealt with by returning 0.
But on UP, zone_page_state will just return a wrapped unsigned long,
which will get past the <= 0 check and then consider the zone eligible
until its watermarks are hit.
Commit 3a025760fc15 ("mm: page_alloc: spill to remote nodes before
waking kswapd") already made the counter-resetting use
atomic_long_read() to accomodate underflows from remote spills, but it
didn't go all the way with it.
Make it clear that these batches are expected to go negative regardless
of concurrency, and use atomic_long_read() everywhere.
Fixes: 81c0a2bb515f ("mm: page_alloc: fair zone allocator policy")
Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Leon Romanovsky <leon@xxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.12+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 18cee0d4c8a2..eee961958021 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1612,7 +1612,7 @@ again:
}
__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
- if (zone_page_state(zone, NR_ALLOC_BATCH) == 0 &&
+ if (atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]) <= 0 &&
!zone_is_fair_depleted(zone))
zone_set_flag(zone, ZONE_FAIR_DEPLETED);
@@ -5701,9 +5701,8 @@ static void __setup_per_zone_wmarks(void)
zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + (tmp >> 1);
__mod_zone_page_state(zone, NR_ALLOC_BATCH,
- high_wmark_pages(zone) -
- low_wmark_pages(zone) -
- zone_page_state(zone, NR_ALLOC_BATCH));
+ high_wmark_pages(zone) - low_wmark_pages(zone) -
+ atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));
setup_zone_migrate_reserve(zone);
spin_unlock_irqrestore(&zone->lock, flags);
--
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